Apparatus and method for strengthening welded-lap joints for steel pipeline

ABSTRACT

An apparatus and method for reinforcing a welded-lap pipe joint includes a first pipe segment having a bell-end presenting a receptacle, a spigot-end of a second pipe segment extending into and welded to the bell-end receptacle to form a welded-lap joint, and a bell-shaped reinforcing sleeve surrounding the welded-lap joint. In exemplary embodiments the reinforcing sleeve is welded to the first or second pipe segments. Also disclosed are a method of assembling a reinforced welded-lap pipe joint.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/210,009 filed on Aug. 26, 2015, and to U.S. ProvisionalApplication Ser. No. 62/378,519 filed on Aug. 23, 2016, each of which ishereby incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

Pipelines are used to transport fluid materials such as liquids orgasses across long distances, over and under land and water. In the U.S.alone, several million miles of pipelines are used to carry water, oil,natural gas, and other resources from one point to another. Pipelinesare typically built as large hollow cylindrical conduits constructed bysuccessively joining individual pipe segments to form a tubular pipelineof virtually any desired length. The material, diameter, and otherphysical characteristics of a pipeline vary depending on the material tobe transported, the required volumetric flow rate to transport, and thestructural and environmental conditions to which the pipeline isexpected to be subjected. For example, steel pipelines having a diameterof over sixty inches are often used to transport large volumetric flowrates of water and other liquids. Steel pipelines having diametersranging from under six inches to over twelve feet are common, withlarger and smaller diameters sometimes used for specific applications.

Because pipelines are routed underground or above ground as necessary,and span vast lengths, they are often subjected to ground inducedactions that apply forces to the pipelines that may threaten theirstructural integrity. For example, seismic events, in the form ofseismic wave actions; or permanent ground deformations, such as a faultmovement, liquefaction-induced settlement/uplifting and lateralspreading, or landslide motion, all induce movement and inflict forcesupon portions of the pipeline. Data collected from pipelines subjectedto earthquakes show that permanent ground deformations are the primarysource of threat for buried pipeline integrity, usually resulting inbending and deformation of portions of the pipeline.

Various standards and criteria applicable to the construction ofpipelines are known and used within the pipeline industry to defineallowable limits and quantify pipeline performance. For example, withrespect to water-carrying pipelines, the primary performance criteria is“no loss of containment” upon occurrence of a seismic or other movementevent. In view of those criteria, pipe segments are not normally linkedby gasket joint systems where significant seismic action is expected,instead the pipe joints are welded to provide a more secure attachmentbetween segments.

Welded pipeline joints may take various forms, including butt-welded,where two plane ends of adjoining pipe segments are aligned and welded,and lap-welded, where an expanded end (bell) of one pipe segment isplaced over a stub end (spigot) of an adjoining pipe segment and welded.Lap welded joints are either single welded (a weld on one end of thespigot or bell) or double welded (a weld on both the bell and spigot-endof the lap joint).

Welded-lap joints have been extensively used in steel water pipelinesrather than butt-welded joints because of they typically have lowerinstallation costs. However, even though more favored for field assemblythan butt-welded joints, industry data shows that welded-lap joints mayconstitute a weak point in the pipeline. Because of their geometry andthe resulting stress path the bell eccentricity creates, under severecompressive loading conditions welded-lap joints are prone tofail—typically in the form of wrinkles occurring as localizeddeformation and folding at the bell eccentricity. This deformation maylead to fracture of the pipeline due to excessive local tensile strainor fatigue under operational loading conditions.

Thus, there remains a need in the art for an improved apparatus andmethod for joining pipe segments in a pipeline to provide superiorstrength, resilience, and resistance to failure under movementconditions.

SUMMARY OF THE INVENTION

An apparatus and method for reinforcing a welded-lap joint for steelpipe includes a first pipe segment having a bell-end presenting areceptacle for receiving a mating spigot-end (i.e., a stub-end), aspigot-end of a second pipe segment extending into and welded to thebell-end receptacle to form a welded-lap joint, and a bell-shapedreinforcing sleeve surrounding the welded-lap joint. In variousexemplary embodiments the first and/or second ends of the reinforcingsleeve is welded to the first or second pipe segments.

In another aspect the present invention is directed to a method ofreinforcing a welded-lap pipe joint by positioning a cylindricalreinforcing sleeve around a cylindrical pipe segment and expanding thepipe end and sleeve simultaneously to form a bell-end on the pipesegment and a bell-shaped reinforcing sleeve surrounding the pipe end.

Various objects and advantages of this invention will become apparentfrom the following description taken in relation to the accompanyingdrawings wherein are set forth, by way of illustration and example,certain embodiments of this invention.

The drawings constitute a part of this specification, include exemplaryembodiments of the present invention, and illustrate various objects andfeatures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a spigot-end to spigot-endpipe joint as known in the prior art.

FIG. 2 is a cross-sectional side view of a spigot-end to spigot-end pipejoint having a full butt-weld as known in the prior art.

FIG. 3 is an exploded perspective view of a spigot-end to bell-end pipejoint as known in the prior art.

FIG. 4 is a cross-sectional side view of a spigot-end to bell-end pipejoint having a lap-weld as known in the prior art.

FIG. 5 is a perspective view of a reinforcing sleeve for a welded-lapspigot-end to bell-end pipe joint in accordance with an exemplaryembodiment of the present invention.

FIG. 6 is an end view of the reinforcing sleeve of FIG. 6

FIG. 7 is a side view of the reinforcing sleeve of FIG. 6.

FIG. 8 is a cross-sectional side view of a reinforced spigot-end tobell-end welded-lap pipe joint with a reinforcing sleeve in accordancewith an exemplary embodiment of the present invention.

FIG. 9 is a cross-sectional side view of a method for making a bell-endpipe and reinforcing sleeve in accordance with an exemplary embodimentof the present invention.

FIG. 10 is a cross-sectional side view of a bell-end pipe andreinforcing sleeve in accordance with an exemplary embodiment of thepresent invention.

FIG. 11 is a schematic representation of a welded-lap joint undercompressive loading.

FIG. 12 is a representation of a mathematical model for analysis of thewelded lap-joint of FIG. 11.

FIG. 13 is a schematic representation of a reinforced welded-lap jointin accordance with an exemplary embodiment of the present inventionunder compressive loading.

FIG. 14 is a representation of a mathematical model for analysis of thereinforced welded-lap joint of FIG. 13.

FIGS. 15 through 21 are graphical representations and comparisons of theresults of three-dimensional finite element analysis of compressiveforce applied to plain pipe, an unreinforced welded-lap joint, and areinforced welded-lap joint in accordance with an exemplary embodimentof the present invention over various operational pressures.

FIGS. 22-24 are graphical representations and comparisons of the resultsof axisymmetric analysis of compressive force applied to an unreinforcedwelded-lap joint, and a reinforced welded-lap joint in accordance withan exemplary embodiment of the present invention over variousoperational pressures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present invention in virtually anyappropriately detailed structure. It should further be understood thatthe features of the invention as depicted and described in the variousexemplary embodiments may be arranged in combinations other than thosespecifically depicted.

Pipelines for carrying liquid, gas, or other flowable materials acrossof land and water are known in the art. A typical steel pipelinecomprises a plurality of hollow cylindrical pipe segments attachedend-to-end, extending over long distances underground, above ground, orunder water. Various methods and means for attaching the pipe segmentsinto a pipeline are known in the art.

For example, FIGS. 1 and 2 depict one known method of attaching first 10and second 12 pipe segments to form a pipeline. Each of the straightpipe segments 10, 12 comprises a hollow cylindrical tube formed by acontinuous wall 14 having a substantially constant thickness t aroundthe circumference of the pipe segment. The continuous wall 14 definesthe pipe segment's inner 16 and outer 18 surfaces. The adjacentcylindrical end portion 20, 22, of each pipe segment is a spigot-end(i.e., a straight or stub-end, not flared or belled), having the sameinner and outer diameters and wall thickness as the main body portion ofthe pipe segment. The face 24 of each pipe segment is a flat ring, lyingin a plane extending generally perpendicular to the corresponding pipesegment's longitudinal axis 26, 28.

Looking to FIG. 2, when joined into a pipeline the two pipe segments 10,12 are aligned along their longitudinal axes 26, 28 and placed togetherend-to-end so that the face of the first spigot-end 20 butts against theface of the second spigot-end 22. Thus positioned, the inner 15 andouter 17 surfaces of the first pipe segment 10 align with thecorresponding inner 16 and outer 18 surfaces of the second pipe segment12 such that the two aligned pipe segments form a single pipeline. Theouter surfaces 17, 18 of the adjacent pipe segments 10, 12 are weldedtogether around the entire circumference of the butt-joint to secure thetwo segments together, with the weld 30 protruding slightly outwardlyfrom the adjoined outer surfaces. Note that the weld 30 depicted in thefigures is illustrative, and does not necessarily reflect an actual ortypical shape or protrusion of a welded butt joint. In practice, the endsurfaces of the adjoining pipe segments may be beveled so that the weldbetween the beveled ends results in only a slight hump or protrusion atthe joint. The end-to-end alignment and welding of subsequent adjoiningpipe segments is repeated to build pipelines of a desired length.

Properly aligned pipe segments joined using a spigot-end to spigot-endwelded butt-joint as just described are effectively as strong as acontinuous pipe segment of the same length having no joints. However,the process of completing such butt-joints in the field is extremelyexacting and labor intensive. In order to achieve a strong joint, thefaces of the adjoining pipe segments must each be formed or cut so thatthe face is substantially perpendicular to the longitudinal axis of thepipe segment. Even when the faces are precisely formed, the longitudinalaxes of the two adjoining pipe segments must be aligned precisely toachieve a uniform fit between the two faces. That configuration must bemaintained while the entire circumference of the joint is welded to jointhe outer surfaces. In some cases, the inner surfaces of the adjoiningpipe segments may likewise be joined by welding in a manner similar todescribed for the outer surfaces. Any variation in the perpendicularityof the faces, relative out-of-roundness of adjoined pipe segments, orany variation in the alignment of the adjoining pipe segments can resultin a non-uniform gap at the joint which potentially results in a weakpoint in the joint.

Furthermore, any desired or intentional misalignment of the adjoiningpipe segments will result in a non-uniform gap at the joint and apotential weakness. For example, if the distal end of the second pipesegment is required to be positioned slightly askew from itsaxially-aligned position, such as to connect to an offset existing lineor fitting, that intentional misalignment necessarily affects thealignment of the faces of the adjoining pipe segments and potentiallycompromises the integrity of the welded butt-joint. Furthermore, the useof a miter at the distal end to achieve the desired alignment offsetmakes it more difficult to fit-up and align the second pipe segmentspigot-end to minimize and achieve the optimal weld gap for a butt-weldjoint.

In order to overcome the difficulties and shortcomings of butt-weldedjoints, pipelines comprised of pipe segments joined using weldedlap-joints such as those depicted in FIGS. 3 and 4 are commonly used inthe industry. Looking to those figures, adjoining pipe segmentsinterconnect by mating a spigot-end 120 of a first pipe segment 110 intoa bell-end 122 of a second pipe segment 112 such that the ends of theadjoined pipes overlap, with the spigot-end inside of the bell-end.

The spigot-end 120 of the pipe segment 110 is essentially identical tothe spigot-end of the straight pipe segments 10, 12 described above withrespect to the prior art of FIGS. 1 and 2, comprising a continuous wallhaving a thickness is and defining an inner and outer surface of thepipe segment 110.

Second pipe segment 112 comprises a smaller diameter main body portion121 that transitions into the larger diameter bell-end portion 122 atthe end of the segment. Main body portion 121 is a straight pipe segmentessentially identical to the straight pipe segments 10, 12 describedabove with respect to the prior art of FIGS. 1 and 2. The bell-endportion 122 is formed at the end of the segment by expanding the end ofthe pipe segment.

As can be seen in FIGS. 3 and 4, the transition between the main bodyportion 121 and the bell-end portion 122 comprises a shallow “S”-shapedtransition area 123 where the wall of the pipe segment flares outwardlyaway from the longitudinal axis and then back toward that axis, into thelarger diameter segment that extends to the end of the pipe segment 112.

As seen in FIG. 4, the inner diameter of the bell-end 122 is slightlylarger than the outer diameter of the spigot-end 120 so that thespigot-end fits into the bell-end 122 receptacle leaving a small gap 125between the outer surface 117 of the spigot-end 120 of the first pipesegment 110 and the inner surface 116 of the bell-end 122 of the secondpipe segment. The width of the gap 125 may vary depending upon theapplication and/or the material being transported in the pipeline. Forexample, for welded steel pipeline carrying water, the American WaterWorks Association (AWWA) Standard C200 calls for the insidecircumference of the bell end to not exceed the outside circumference ofthe spigot end by more than 0.400 inches. Preferably, the width of gap125 is less than 0.400, most preferably the width is approximately 0.200inches.

Looking still to FIG. 4, the lap joint is assembled by placing thespigot-end 120 of the first pipe segment 110 into the bell-end 122 ofthe second pipe segment 112 such that there is an overlap 129 of the twopipe segments. The overlap 129 between the two pipe segments may varydepending upon the application and/or the material being transported inthe pipeline. For example, for welded steel pipeline carrying water,AWWA Standard C206 calls for an overlap of one inch, or three times thethickness of the belled pipe, whichever is greater. Thus, preferably,the overlap 129 is the greater of one inch or three times the thicknessof the belled pipe. Most preferably, the overlap 129 is betweenapproximately three inches and five inches to accommodate temperaturefluctuations.

The end face of the bell-end 122 is typically welded 130 to the outersurface 117 of the spigot-end 120 around the outer circumference of thefirst pipe segment 110 to secure the two segments together. In manycases the end face of the spigot-end 120 is welded 131 to the interiorsurface 116 of the bell-end 122 around the interior joint between thetwo joined pipe segments. Thus, depending on which end faces are welded,a welded-lap joint is commonly referred to as a single-weld ordouble-weld joint. The apparatus and system of the present invention isnot restricted to use with either single-weld or double-weld lap joints,although double-weld lap joints are predominate in the industry.

The welded-lap joint just described is more widely used in pipelineconstruction than the butt-joint previously described as a welded-lapjoint is generally easier to assemble in the field and is more tolerantof variations in the axial alignment of adjacent pipe segments.

The present invention is directed to a reinforcing sleeve apparatus andmethods for reinforcing a welded-lap pipe joint as will now be describedwith respect to various exemplary embodiments. Looking to FIGS. 6through 8, a sleeve for reinforcing a welded-lap pipe joint inaccordance with an exemplary embodiment of the present invention isdepicted generally by the numeral 200. The sleeve 200 comprises abell-shaped elongated body extending between a smaller diameter firstend 202 and a larger diameter second end 204.

The shape of the reinforcing sleeve is generally frustoconical, taperingfrom a smaller diameter first end to a larger diameter second end, withthe bell shape defined by the transition from a smaller diameter firstsegment 206 (extending inwardly from the first end 202), through an“S”-shaped (in profile) transition segment 210, to a larger diametersecond segment 208 extending to the second end 204. As best seen in theside view of FIG. 8, the transition segment flares outwardly away fromthe longitudinal axis 212 of the sleeve at the end of the first segment206 and back towards the longitudinal axis 212 at the beginning of thesecond segment 208 such that the diameter of the sleeve increases fromthe first end 202 to the second end 204.

The first 214 and second 216 faces of the sleeve each lie in a planesubstantially perpendicular to the longitudinal axis 212 of the sleeveso that the two faces 214, 216 lie substantially parallel to each other.The sleeve has an overall length L, and an outer diameter d.

The length L of the sleeve can vary depending on the application, in oneembodiment, the sleeve preferably extends from within one wall thicknessof the end of the bell, through the “S” shape of the bell, and onto thestraight pipe for at least approximately twelve inches. The outerdiameter d of the sleeve is preferably sized such that it is larger thanthe parent pipe prior to expanding.

In other embodiments, the ratio of the length of the “S”-shapedtransition portion 210 to the outer diameter d is approximately 0.03. Infurther embodiments, the length of the transition portion 210 isapproximately two inches.

The sleeve 200 thus comprises a continuous outer wall 218 defining aninterior surface 220 and an exterior surface 222, formed as a bell-shapehaving the properties just described.

Preferably, sleeve 200 is configured and shaped such that the interiorsurface 220 conforms closely to the shape of the outer surface of abell-end portion of a welded-lap joint comprising a spigot-end tobell-end pipe joint as previously described.

Most preferably, sleeve 200 is made of steel having the same propertiesof the pipe which it is being used to reinforce.

Turning to FIG. 9, an exemplary embodiment of an apparatus and methodfor reinforcing a welded-lap pipe joint in accordance with the presentinvention using a reinforcing sleeve as just described is depictedgenerally by the numeral 300. A welded-lap pipe joint configured in amanner similar to that as previously described with respect to the priorart of FIGS. 3 and 4 comprises a first pipe segment 310 having aspigot-end and a second pipe segment 312 having a bell-end receptacle.The spigot-end is inserted into the bell end so that there is an overlap314 between the two pipe segments, and the two segments are welded witheither a single or double weld 316 a, 316 b as previously described.

A bell-shaped reinforcing sleeve 318, in accordance with the exemplaryembodiment previously described with respect to FIGS. 3 and 4, ispositioned over the bell-end of the second pipe segment. The shape anddiameter along the length of the inner surface of the sleeve 318preferably conforms closely to the shape and diameter along thecorresponding length of the outer surface of the bell-end receptacle ofthe second pipe segment 312 so that the sleeve fits tightly over thesecond pipe segment.

Most preferably, the diameter of the outer surface of the bell-end ofthe of the second pipe segment 312 is approximately equal to thecorresponding inner diameter of the sleeve 318 such that there is nogap, or minimal gap, between the two along the bell portion. Inalternative embodiments, a gap may be formed between the inner surfaceof the sleeve and the outer surface of the bell-end of the second pipesegment along the inward portion of the sleeve, such as along thestraight pipe portion of the second pipe segment.

As will be discussed in more detail below, in one exemplary embodimentthe sleeve 318 is formed by expanding the bell-end of the second pipesegment and the sleeve simultaneously, thus the inner surface of thesleeve conforms closely to the outer surface of the bell-end.

The wall thickness of the reinforcing sleeve may be varied depending onthe structural requirements of the pipeline. Preferably, the wallthickness of the reinforcing sleeve 318 is substantially the same as thewall thickness of the bell-end portion of the second pipe segment 312.

It should be understood that the reinforcing sleeve 318 achieves itsincrease in the strength of the welded-lap pipe joint by encompassingthe joint, and that the reinforcing sleeve need not be attached orwelded to the first or second pipe segments, it may remain in positionthrough frictional engagement with the bell-end of the second pipesegment. In alternative embodiments, and as depicted in FIG. 9, thesmaller diameter end of the reinforcing sleeve 318 is welded 322 to theouter surface of the second pipe segment 312 to prevent the sleeve frommoving from its position overlapping the pipe joint.

In other alternative embodiments, the reinforcing sleeve 318 may bewelded at its larger diameter end to the bell-end of the second pipesegment 312 to maintain the sleeve in its overlapping position. In yetother alternative embodiments, the reinforcing sleeve 318 may be weldedat both ends to the second pipe segment 312 to prevent moisture ordebris from entering the gap between the reinforcing sleeve 318 and thesecond pipe segment 312.

It should be further understood that in one embodiment of the presentinvention the reinforcing sleeve is manufactured separately from thepipes comprising the welded-lap joint and is positioned into place overthe pipes prior to or subsequent to completing the welded-lap joint. Inanother embodiment of the present invention as will now be describedwith reference to FIGS. 9 and 10, the reinforcing sleeve is formedcontemporaneously with the bell-end portion of the pipe segment.

Looking to FIGS. 9 and 10, a cylindrical sleeve 410 is positioned arounda section of cylindrical straight pipe 412, adjacent an end 414 of thepipe segment. Similar to the cylindrical pipe segments describedpreviously, the sleeve 410 and the pipe segment 412 each comprise acontinuous wall 416 and 418, respectively, each wall having acorresponding thickness t1, t2. In the exemplary embodiment depicted thewall thickness t1 of the sleeve 410 and the wall thickness t2 of thepipe segment 412 are substantially identical. In alternativeembodiments, the thickness of the walls may vary.

The continuous wall 416 of the sleeve defines the interior 420 andexterior 422 surfaces of the sleeve, and the continuous wall 418 of thepipe segment defines the interior 424 and exterior 426 surfaces of thepipe segment. Preferably, the interior diameter of the sleeve 410conforms closely to the exterior diameter of the pipe segment. Mostpreferably, the gap between the inside surface of the reinforcing sleeveand the outside surface of the pipe end before expansion is inconformance with AWWA Standard C200, as discussed above to allowinsertion of the spigot-end into the sleeve.

As depicted in the embodiment of FIG. 9, the cylindrical sleeve 410 ispositioned adjacent an end 414 of the pipe segment 412, with the sleeve410 entirely overlapping the segment such that no portion of the sleeveextends beyond the end 414 of the pipe segment. Most preferably, theouter end of the sleeve 410 is positioned inwardly from the outer end414 of the pipe segment within a distance equal to the thickness a ofthe sleeve.

With the sleeve 410 thus positioned over the pipe segment 412 adjacentthe end 414, the end portion of the pipe segment is expanded to form abell-end receptacle and to simultaneously form the overlying cylindricalsleeve 410 into a bell-shape.

In one exemplary embodiment as depicted in FIG. 9 the pipe segment 410end is swaged by pressing the end of the pipe segment over and onto abell shaped die 428 (or by pressing the die 428 into the end of the pipesegment to expand the end of the pipe segment 412 and the overlyingcylindrical sleeve 410 to conform to the shape of the outer surface ofthe die 428. The pipe and/or die are pressed together using a hydraulicpress or other swaging tool known in the art. In addition, the pipesegment, the die, or both may be rotated to facilitate the expansion.Alternatively, the end of the pipe and overlying sleeve can be expandedto a bell-end receptacle using a hydraulic expansion tool.

Regardless of the method or tool used to expand the pipe end and sleeve,the result, as depicted in FIG. 10, is a bell-end receptacle 430 formedin the end of the pipe segment 410, and a bell-shaped reinforcing sleeve432 formed from the expanded cylindrical sleeve.

Advantageously, because the reinforcing sleeve is formed simultaneouslywith and by the expansion of the end of the pipe segment, the interiorsurface of the reinforcing sleeve conforms closely to the exteriorsurface of the pipe segment. Most preferably, after expansion there isno gap between the outer surface of the bell-end receptacle 430 and theinner surface of the reinforcing sleeve 432.

As will be apparent to those skilled in the art, in alternativeembodiments, the sleeve 410 may be longer than depicted and thus mayextend over a longer portion of the pipe segment such that at least aportion of sleeve 410 is not expanded by the die. In those embodiments,a gap may exist between the inner surface of the sleeve and the outersurface of the pipe segment along the non-expanded portions. Preferablythe dimension of the gap in those portions conforms to AWWA StandardC200 as discussed previously. It should be further understood that,depending on the length of the die 428 and the length of thenon-expanded sleeve 410, and the depth to which the die is inserted intothe pipe segment and the sleeve, that a gap may exist between the innersurface of the expanded reinforcing sleeve 432 and the outer surface ofthe pipe segment. These and other variations are within the scope of thepresent invention.

Similarly, because the bell-end of the pipe segment and the bell shapeof the reinforcing sleeve are formed at the same time from the same dieor expansion, any variations in the die or expansion tool are replicatedon both the pipe end and the reinforcing sleeve, avoiding variances thatmay occur if the reinforcing sleeve is manufactured separately from thebell-end of the pipe.

With the bell-shaped reinforcing sleeve 432 formed and positioned aroundthe bell-end receptacle 430 as just described, the welded-lap jointbetween the bell-end receptacle and a spigot-end pipe segment can becompleted in a manner as previously described. When the joint iscomplete, the reinforcing sleeve 432 is positioned around the joint aspreviously described to reinforce and strengthen the joint. As alsopreviously described, the reinforcing sleeve can be welded at one orboth ends to secure the sleeve to the bell-end pipe segment.

The effectiveness of the reinforcing sleeve and the method ofreinforcing welded-lap pipe joints of the present invention as justdescribed is demonstrated by comparison of numerical and graphicalresults of two and three-dimensional modeling and finite elementanalysis performed on models of various configurations of plain straightpipes (i.e., pipe segments with no joints), unreinforced spigot-end tobell-end welded-lap pipeline joints, and reinforced spigot-end tobell-end welded-lap joints in accordance with the present invention.

Looking to FIGS. 11 and 13, schematic representations of a welded-lapjoint and a reinforced welded-lap joint in accordance with an exemplaryembodiment of the present invention are depicted. A compressive loadapplied to the welded-lap joint is represented in each schematic by adifferential rotation between the two jointed pipes. As depicted by therotational arrows at each end of the schematic diagram, a rotation ofeither one of the joined pipes, or a differential in the rotation ofboth pipes will result in a compressive load applied to the respectivewelded-lap joint.

FIGS. 12 and 14 are representations of the mathematical models used toanalyze the respective unreinforced and reinforced welded-lap pipejoints. The parameters identified in those models and the initialconditions used in the analysis are set forth in Table 1 as follows:

TABLE 1 D (in) 67.75 Pipe outer diameter t (in) 0.375 Pipe thicknesst_(r) (in) 0.375 Over-fit part thickness s (in) 2.0 Length of straightpart of over-fit part d (in) 3.0 Distance between pipe welds L_(S1) (in)1.375 Distance between internal pipe weld and curved part. L_(S2) (in)1.375 Distance of over-fit bell from external pipe weld. L_(b) (in) 5Pipe bell length g (in) 0.03-0 Gap between over-fit part and pipe c (in)0.05 Gap between pipe bell and pipe spigot e (in) 0.50 Jointeccentricity

For purposes of the analysis, it is assumed that the first and secondpipe segments and the reinforcing sleeve are made from grade 40 steelwith yield stress equal to 43.9 ksi (303 MPa), that the welded-lap jointitself is double welded (i.e., welded on both the interior and exteriorof the joint as described above), and that the nominal outer diameter ofthe spigot-end pipe segment is 67.75 inches with a wall thickness of0.375 inches, corresponding to a diameter-to-thickness ratio of 180. Asdescribed in more detail below, analyses for a single-weld reinforcingsleeve and a double-weld reinforcing sleeve (as opposed to thedouble-weld lap joint) are performed.

FIGS. 15 through 22 depict and compare the results of plain pipes,unreinforced weld-lap joint pipes, and reinforced weld-lap pipe jointsin accordance with the present invention subjected to varying bendingmoments applied and the resulting bending curvatures, over a range ofoperating yield pressures. The normalized bending moment/curvaturegraphs illustrate the point at which the pipe buckles, represented bythe sudden drop or break in the data line corresponding to thatanalysis.

Looking first to FIG. 15, the results of applying an increasing bendingmoment to a plain pipe (i.e., a pipe with no joints whatsoever) areshown. Looking to FIG. 15, it can be seen that for a normalized bendingmoment of up to approximately 0.6, the normalized curvature of thestraight pipe follows linearly over all ranges of internal yieldpressure from 0 percent to 40 percent.

At a normalized bending moment of approximately 0.65 the 0 percent yieldpressure pipe buckles as indicated by line 500, with the 10 percent, 20percent, 30 percent, and 40 percent yield pressure cases following insuccession as the normalized bending moment increases to approximately0.75 as indicated by lines 502, 504, 506, and 508, respectively.

Turning to FIG. 16, the same analysis is performed for an unreinforcedwelded-lap joint. As seen in the graph, for a normalized bending momentof up to approximately 0.45, the normalized curvature of theunreinforced welded-lap joint follows linearly over all ranges ofinternal yield pressure from 0 percent to 40 percent.

At that normalized bending moment of approximately 0.45 the 0 percentyield pressure pipe buckles as indicated by line 510, with the 10percent, 20 percent, 30 percent, and 40 percent yield pressure casesfollowing in succession as the normalized bending moment increases toapproximately 0.75 as indicated by lines 512, 514, 516, and 518,respectively.

Looking to FIG. 17, the analysis is performed for a reinforcedwelded-lap joint (i.e., a reinforced joint having a reinforcing sleevein accordance with the present invention) where the reinforcing sleeveis welded to the bell-end pipe segment only at one end of the sleeve. Asseen in the graph, for a normalized bending moment of up toapproximately 0.6, the normalized curvature of the unreinforcedwelded-lap joint follows linearly over all ranges of internal yieldpressure from 0 percent to 40 percent.

At a normalized bending moment of approximately 0.63 the 0 percent yieldpressure pipe buckles as indicated by line 520, with the 20 percent, 30percent, and 40 percent yield pressure cases following in succession asthe normalized bending moment increases to approximately 0.75 asindicated by lines 522, 524, and 526, respectively.

FIG. 18, depicts the results of the analysis performed for a reinforcedwelded-lap joint (i.e., a reinforced joint having a reinforcing sleevein accordance with the present invention) where the reinforcing sleeveis welded to the bell-end pipe segment at both ends of the reinforcingsleeve. As seen in the graph, for a normalized bending moment of up toapproximately 0.6, the normalized curvature of the unreinforcedwelded-lap joint follows linearly over all ranges of internal yieldpressure from 0 percent to 40 percent.

At a normalized bending moment of approximately 0.65 the 0 percent yieldpressure pipe buckles as indicated by line 530, with the 20 percent and40 percent yield pressure cases following in succession as thenormalized bending moment increases to approximately 0.75 as indicatedby lines 532, and 534, respectively

Looking to FIGS. 19 through 21, the results of the analyses justdescribed for the unreinforced, reinforced and double-weld reinforcedare compared for the 0 percent, 20 percent, and 40 percent yieldpressure cases.

As seen in FIG. 19, for the 0 percent yield pressure case both thesingle-weld reinforced joint 542 and the double-weld reinforced joint544 substantially outperform the unreinforced joint 540, with thedouble-weld reinforced joint outperforming the single-weld reinforcedjoint.

FIGS. 20 and 21 depict similar results for the 20 percent and 40 percentyield pressure cases, respectively. As seen in FIG. 20, the single-weld552 and double-weld 554 reinforced joints substantially outperform theunreinforced lap joint 550, and as seen in FIG. 21, the single-weld 562and double-weld 564 reinforced joints similarly outperform theunreinforced lap joint 560.

Turning to FIGS. 22 through 24, similar results of an axisymmetric modelanalysis is depicted.

As seen in FIG. 22, for an unreinforced welded-lap pipe joint, anapplied axial load over varying yield pressures results in linear axialdisplacement up until the point that the joint buckles. For thatunreinforced joint, at 0 percent yield pressure the buckling occurs at anormalized axial load of approximately 0.55 F/Fp as indicated by line570, with the 10 percent, 20 percent, 30 percent, and 40 percent yieldpressure cases following in succession as indicated by lines 572, 574,576, and 578, respectively.

FIG. 23 presents the results of the analysis applied to a reinforcedwelded-lap pipe joint in accordance with the present invention over thatsame range of yield pressures. As indicated by lines 580, 582, 584, 586,and 588 the reinforced joint substantially outperforms the unreinforcedjoint, with the 0 percent yield pressure case 580 not buckling until anormalized axial load of approximately 0.75 is reached.

FIG. 24 compares the analysis data just discussed on a single graph forthe 0 percent yield case which demonstrates that the reinforcedwelded-lap joint 592 of the present invention substantially outperformsan unreinforced welded-lap joint 590.

From the foregoing it will be seen that this invention is one welladapted to attain all ends and objectives herein-above set forth,together with the other advantages which are obvious and which areinherent to the invention.

Since many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that allmatters herein set forth or shown in the accompanying drawings are to beinterpreted as illustrative, and not in a limiting sense.

The term “substantially” or “approximately”, or any other qualifyingterm as used herein may be applied to modify any quantitativerepresentation which could permissibly vary without resulting in achange in the basic function to which it is related. For example, in oneembodiment the thicknesses of the wall of the pipe end and the wall ofthe reinforcing sleeve are described as being substantially identical,but may permissibly vary from that configuration if the variance doesnot materially alter the capability of the invention.

With respect to the steps of any method described herein or in theaccompanying claims, no specific ordering of those steps is implied bythe order in which those steps are described or claimed, and unlessexplicitly required the steps may be performed in any order inaccordance with the present invention.

While specific embodiments have been shown and discussed, variousmodifications may of course be made, and the invention is not limited tothe specific forms or arrangement of parts and steps described herein,except insofar as such limitations are included in the following claims.Further, it will be understood that certain features and subcombinationsare of utility and may be employed without reference to other featuresand subcombinations. This is contemplated by and is within the scope ofthe claims.

Additional aspects of the invention, together with the advantages andnovel features appurtenant thereto, will be set forth in part in thedescription which follows, and in part will become apparent to thoseskilled in the art upon examination of the following, or may be learnedfrom the practice of the invention. The objects and advantages of theinvention may be realized and attained by means of the instrumentalitiesand combinations particularly pointed out in the appended claims.

Having thus described the invention what is claimed as new and desiredto be secured by Letters Patent is as follows:
 1. A reinforcedwelded-lap pipe joint, comprising: a first pipe segment comprising abell-end presenting a receptacle for receiving a mating spigot-end; asecond pipe segment having a spigot-end, a portion of the spigot-endextending into and welded to the bell-end; and a bell-shaped reinforcingsleeve extending between a smaller diameter first end and a largerdiameter second end, the reinforcing sleeve positioned at leastpartially over and surrounding the bell-end of the first pipe segmentsuch that the sleeve overlaps a portion of each of the first and secondpipe segments.
 2. The reinforced welded-lap pipe joint of claim 1,wherein the bell-shaped reinforcing sleeve is welded to at least one ofthe first and second pipe segments.
 3. The reinforced welded-lap pipejoint of claim 2, wherein the larger diameter second end of thebell-shaped reinforcing sleeve is welded to the first pipe segment. 4.The reinforced welded-lap joint of claim 2, wherein the smaller diameterfirst end of the bell-shaped reinforcing sleeve is welded to the firstpipe segment.
 5. The reinforced welded-lap joint of claim 2, wherein thesmaller diameter first end and the larger diameter second end of thebell-shaped reinforcing sleeve are welded to the first pipe segment. 6.The reinforced welded-lap pipe joint of claim 2, wherein the largerdiameter second end of the bell-shaped reinforcing sleeve is welded tothe first and second pipe segments.
 7. The reinforced welded-lap pipejoint of claim 2, wherein the smaller diameter first end of thebell-shaped reinforcing sleeve is welded to the first pipe segment andthe larger diameter second end of the bell-shaped reinforcing sleeve iswelded to the first and second pipe segments.
 8. The reinforcedwelded-lap joint of claim 2, wherein the first pipe segment is welded tothe second pipe segment along an exterior surface of the first pipesegment.
 9. The reinforced welded-lap joint of claim 2, wherein thefirst pipe segment is welded to the second pipe segment along aninterior surface of the first pipe segment.
 10. The reinforcedwelded-lap pipe joint of claim 1 wherein the bell-shaped reinforcingsleeve comprises a wall having a thickness substantially the same as awall of the first pipe segment.
 11. The reinforced welded-lap pipe jointof claim 1, wherein the bell-shaped reinforcing sleeve overlaps thespigot-end to bell-end weld.
 12. The reinforced welded-lap pipe joint ofclaim 1, wherein the bell-shaped reinforcing sleeve has a length ofapproximately 0.03 times a diameter of the bell-end of the first pipesegment.
 13. The reinforced welded-lap pipe joint of claim 1, whereinthe bell-shaped reinforcing sleeve has a length of approximately atleast 2 inches.
 14. A method for reinforcing a welded-lap pipe joint,comprising: providing a first pipe segment comprising a bell-end, thebell-end presenting a receptacle for receiving a mating spigot-end;inserting a spigot-end of a second pipe segment into the bell-endreceptacle; welding the spigot-end of the second pipe segment to thebell-end of the first pipe segment; and placing a bell-shapedreinforcing sleeve extending between a smaller diameter first end and alarger diameter second end around the bell-end of the first pipe segmentsuch that the sleeve overlaps a portion of each of the first and secondpipe segments.
 15. The method of claim 14, further comprising weldingthe bell-shaped reinforcing sleeve to at least one of the first andsecond pipe segments.
 16. The method of claim 15, wherein the weldingthe bell-shaped reinforcing sleeve step comprises welding the largerdiameter second end of the sleeve to the first pipe segment.
 17. Themethod of claim 15, wherein the welding the bell-shaped reinforcingsleeve step comprises welding the smaller diameter first end of thesleeve to the first pipe segment.
 18. The method of claim 15, whereinthe welding the bell-shaped reinforcing sleeve step comprises weldingthe larger diameter second end of the bell-shaped reinforcing sleeve tothe first and second pipe segments.
 19. The method of claim 15, whereinthe welding the bell-shaped reinforcing sleeve step comprises weldingthe smaller diameter first end of the bell-shaped reinforcing sleeve tothe first pipe segment and welding the larger diameter second end of thebell-shaped reinforcing sleeve to the first and second pipe segments.20. The method of claim 15, wherein the welding the bell-shapedreinforcing sleeve step comprises welding the smaller diameter first endand the larger diameter second end of the sleeve to the first pipesegment.
 21. The method of claim 15, wherein the bell-shaped reinforcingsleeve comprises a wall having a thickness substantially the same as awall of the first pipe segment.
 22. The method of claim 15, wherein thefirst pipe segment is welded to the second pipe segment along anexterior surface of the first pipe segment.
 23. The method of claim 14,wherein the first pipe segment is welded to the second pipe segmentalong an interior surface of the first pipe segment.
 24. The method ofclaim 14, wherein the bell-shaped reinforcing sleeve is positioned suchthat it overlaps the spigot-end to bell-end weld.
 25. The method ofclaim 14, wherein the bell-shaped reinforcing sleeve has a length ofapproximately 0.03 times a diameter of the bell-end of the first pipesegment.
 26. The method of claim 14, wherein the bell-shaped reinforcingsleeve has a length of approximately at least 2 inches.
 27. A method forreinforcing a welded-lap pipe joint, comprising: placing a cylindricalsleeve around a cylindrical first pipe segment adjacent an end of thesegment such that the sleeve entirely overlaps the first pipe segment;expanding the end of the first straight pipe segment and the surroundingsleeve to form a bell-end receptacle at the end of the first straightpipe segment and to shape the cylindrical sleeve into a bell-shapedreinforcing sleeve; inserting a spigot-end of a second pipe segment intothe bell-end receptacle; welding the spigot-end of the second pipesegment to the bell-end of the first pipe segment; and positioning thebell-shaped reinforcing sleeve along the bell-end of the first pipesegment such that the sleeve overlaps a portion of each of the first andsecond pipe segments.
 28. The method of claim 27, further comprisingwelding the bell-shaped reinforcing sleeve to at least one of the firstand second pipe segments.
 29. The method of claim 28, wherein thewelding the bell-shaped reinforcing sleeve step comprises welding thelarger diameter second end of the sleeve to the first pipe segment. 30.The method of claim 28, wherein the welding the bell-shaped reinforcingsleeve step comprises welding the smaller diameter first end of thesleeve to the first pipe segment.
 31. The method of claim 28, whereinthe welding the bell-shaped reinforcing sleeve step comprises weldingthe smaller diameter first end and the larger diameter second end of thesleeve to the first pipe segment.
 32. The method of claim 28, whereinthe welding the bell-shaped reinforcing sleeve step comprises weldingthe larger diameter second end of the bell-shaped reinforcing sleeve tothe first and second pipe segments.
 33. The method of claim 28, whereinthe welding the bell-shaped reinforcing sleeve step comprises weldingthe smaller diameter first end of the bell-shaped reinforcing sleeve tothe first pipe segment and welding the larger diameter second end of thebell-shaped reinforcing sleeve to the first and second pipe segments.34. The method of claim 28, wherein the first pipe segment is welded tothe second pipe segment along an exterior surface of the first pipesegment.
 35. The method of claim 28, wherein the first pipe segment iswelded to the second pipe segment along an interior surface of the firstpipe segment.
 36. The method of claim 27, wherein the bell-shapedreinforcing sleeve comprises a wall having a thickness substantially thesame as a wall of the first pipe segment.
 37. The method of claim 27,wherein the bell-shaped reinforcing sleeve is positioned such that itoverlaps the spigot-end to bell-end weld.
 38. The method of claim 27,wherein the bell-shaped reinforcing sleeve has a length of approximately0.03 times a diameter of the bell-end of the first pipe segment.
 39. Themethod of claim 27, wherein the bell-shaped reinforcing sleeve has alength of approximately at least 2 inches.
 40. The method of claim 20,wherein the expanding step comprises swaging the end of the first pipesegment.
 41. The method of claim 20, wherein the expanding stepcomprises using a hydraulic expander tool to expand the end of the firstpipe segment.
 42. A method for manufacturing a reinforcing sleeve for awelded-lap pipe joint, comprising: placing a cylindrical sleeve around acylindrical first pipe segment adjacent an end of the segment such thatthe sleeve entirely overlaps the first pipe segment; and simultaneouslyexpanding the end of the first straight pipe segment and the surroundingsleeve to form a bell-end receptacle at the end of the first straightpipe segment and to shape the cylindrical sleeve into a bell-shapedreinforcing sleeve.
 43. The method of claim 42, wherein the expandingstep comprises swaging the end of the first pipe segment.
 44. The methodof claim 42, wherein the expanding step comprises using a hydraulicexpander tool to expand the end of the first pipe segment.